Friday, March 30, 2012

A Brief History of the Light Water Reactor to Three Mile Island

The Light Water Reactor is both cooled and moderated by purified ordinary water. Heavy water is water that contains a large amount of Duterium, however it is a better moderator than Light Water. It is far more expensive to produce. Moderators determine how much U-235 is required to start a chain reaction. A reactor that is moderated by heavy water or graphite can produce a chain reaction in purified uranium, while a light water reactor requires uranium enriched to 3% U-235. The enrichment level can actually be lower, but this requires more frequent refulings.

Alvin Weinberg is given credit for inventing the Light Water Reactor. In addition to inventing the Light Water Reactor Concept, Weinburg oversaw the building of the first Light Water Reactor, The Low Intensity Test Reactor. The Reactor was origionally a mock-up intended to be used for training purposes, but not to go critical. The Oak Ridge National Laboratory history 0f its 13 reactors states:

In 1949, while the MTR was being designed, a full-scale mock-up of its major components was built in the middle of the ORNL campus to check out mechanical and hydraulic operation and provide training for operators. But once the mock-up was running, the Laboratory argued that it should be made critical with real fuel plus beryllium reflector elements, which would allow nuclear measure- ments and testing of instruments and controls. This was done, and in 1950, many low-power measurements of importance to the final MTR design were made. In 1952, it was a small step to add shielding and a heat exchanger, providing the Laboratory with the 1500 kW Low-Intensity Test Reactor (LITR). Later, after some modifications, the LITR was operated at 3 MW.

As seen in Fig. 35, the reactor tank was surrounded by concrete blocks, and control-rod drives were mounted on the top. Six horizontal beam tubes were added, and some space in the 5 × 9 core lattice was available for higher flux experiments. Two pneumatic “rabbit” tubes added and removed samples from the reflector.

In one set of tests, the water flow through the core was reduced and it was allowed to boil to observe the effects on stability and control. Those tests presaged later experiments in Idaho that led to boiling-water power reactors. An important and difficult experiment carried out on the LITR was the measurement of the cross section of intensely radioactive xenon-135 as a function of energy.

The LITR was the ancestor of all LWRs.

In the early years after World War II, ORNL ran a school dedictated to reactor science. Weinberg was one of the teachers. The Navy was interested in nuclear reactors to power warships. One officer the Navy sent to study at the school of nuclear science was Hyman Rickover.

In a conversation with Weinberg, Rickover learned of the LWR, and its potential. When Rickover returned to his naval duties he imediately recommended that the Navy undertake a rapid LWR development program. The cold war was underway and an atomic powered submarine would give the Navy a huge advantage over Soviet submarines. The Navy proceeded with a rapid development and by 1953 A prototype reactor had been developed. By January 1955 the first nuclear submarine, the USS Nautilus was operational.

in 1953 President Eisenhower announced his Atoms for Peace policy. Hyman Rickover had a program to develop a prototype reactor that would serve as a tool for the development of nuclear powered aircraft carriers. Experiment with this reactor were not inconsistent with its use to generate electricity. The Duquesne Light Company approached Rickover with a proposal that he provide a reactor to generate electricity for them. Rickover knew that the production of electricity was not inconsistent with the experiments the Navy planned to run with the reactor. Rickover agreed to The Duquesne Light Company's request, and the reactor began generating electricity in late Decenber 1957.

My Father, C. J. Barton, Sr. had made a notable contribution to the LWR. Zarconium was an ideal candidate for fuel cladding in LWRs. Fuel cladding preforms important functions in most reactors. However, although theory suggested Zirconium was ideal for use in reactors, tests showed that Zurconium samples placed inside test reactors absorbed two many of the neutrons that were needed to keep a reactor critical. Oak Ridge Scientists soon discovered the cause, Zarconium always came with some Hafnium, an element that tends to absorb neutrons. My father who worked for the Y-12 plant at the time, discovered a way to seperate Zarconium and Hafnium. Almost every reactor that exists now contains Zarconium.

In 1955 a group of ORNL chemists led by the highly regarded George Parker, began to study reactor safety. In 1960, my father, who was concerned about safety issues, and had solved some glovebox safety problems, joined Parker's group. Gloveboxes were used both by by researchers, and by weapons manufacturers. My father, a scientist who was trained in the old school, had been assigned to do research with plutonium. Plutonium was dangerous because it caught on fire in ordinary air, and then there was hell to pay. There had been a series of fires in gloveboxes used to prepare plutonium at nuclear weapons manufacturing plants. My father was concerned about his personal safety and the safety of other workers in his lab, so he decided to solve the glovebox problem first. He then proceeded to build a safer glovebox and his report was regarded as very helpful by the AEC. The AEC offered kudos to ORNL for my father's work, and he was rewarded by getting to pick his next assignment. He decided to join George Parker in researching nuclear safety. While Parker and his team looked at what happened inside a reactor during a nuclear accident, my father studied what happened to radio isotopes once they escaped a reactor during an accident.

By 1964 AEC research Director Milton Shaw had begun cracking down on nuclear safety research and researchers. My father and Parker ran an annual conference on nuclear safety that attracted scientists from all over the world. Shaw ordered the cancellation of the conference. My father, reading the handwriting on the wall decided to find another project to work on. Within a few years, Shaw completely shut down all nuclear safety research, transferring funds meant to finance safety research to a pet project.

By this time LWRs were getting built in increasing numbers. Shaw pronounced the LWR a mature technology, and was astonished when both scientists and members of the general public begain to protest against Shaw's attitude toward nuclear safety. Then president Nixon appointed Dixie Lee Ray AEC chairman. Ray changed Shaw's job description, removing nuclear safety from his area of responsibility. Shaw quickly resigned as AEC research director, but the damage had been done. Even though the AEC ordered new safety features, causing reactors to be modified or in some cases rebuilt, serious safety defects remained in LWRs as of 1979.

In 1979 there was a serious reactor accident at a place called Three Mile Island. Subsequent research revealed a number of serious safety defects, most of which had been identified before the accident, but which the NRC had not ordered corrections to be made. Only after the lessons of Three Mile Island accident had been assimulated, and reactors had undergone further modification, did the LWR begin to approach maurity.